Electric lamp with heat reflector

ABSTRACT

AN IMPROVED HIGH WATTAGE LAMP WHERE AN EXTERNAL REFLECTIVE COATING OF A REFRACTORY OXIDE IS UTILIZED TO SEPARATE THE FILAMENT ASSEMBLY FROM THE SEAL. THE COATING REFLECTS THE HEAT FROM THE FILAMENT AWAY FROM THE SEAL AREA, THEREBY PROVIDING   A COOLER SEAL AND ALSO DIRECTS STRAY LIGHT RAYS BACK TO THE OPTICAL SYSTEM.

United States Patent 1,967,852 7/1934 Wright 3l3/282X 2,098,080 1l/l937 Wright 174/5063 2,221,868 11/1940 Geiger.... 174/5063 2,241,505 5/1941 Cuttler 174/5063 2,269,840 1/1942 Anderson.. 174/5063 2,407,979 9/1946 Findley 174/5063 2,407,998 9/1946 Richardson 174/5063 2,504,522 4/1950 Greiner 174/5063 3,320,352 5/1967 Kershan 3 l 3/290X 3,209,188 9/1967 Freeman 313/43 Primary Examiner-John W. Huckert Assistant Examiner-Barry Estrin Att0rneys Norman J. OMalley and Laurence Burns ABSTRACT: An improved high wattage lamp where an exter' nal reflective coating of a refractory oxide is utilized to separate the filament assembly from the seal. The coating reflects the heat from the filament away from the seal area, thereby providing a cooler seal and also directs stray light rays back to the optical system.

PATENTEU JUN28|97| 3,588,564

INVENTOR JOHN J. VETERE WM M ATTORNEY ELECTRIC LAMP WITH HEAT REFLECTOR BACKGROUND OF THE INVENTION This invention relates to lamps having tungsten filaments enclosed in sealed envelopes, the latter being of fused quartz or other suitable glass. Such devices generally contain a halogen, such as iodine or bromine, and are usually called halogen-quartz lamps. They operate on a regenerative cycle, initiated when a tungsten halide is produced and chemically combines with the particles evaporated from the incandescing tungsten filament. Subsequent thermal decomposition of this compound replaces the tungsten particles on the filament. More particularly, this invention concerns an improved method of sealing quartz lamps adapted to be bperational with high current loadings of the type described above.

Such high current lamps have many uses especially in the fields of motion pictures, television, photography and infrared heating. In these industries, an ever-increasing demand for more illumination has burdened the lamp manufacturer with added design problems. To appreciate these problems, it must be recognized that in the past, when the wattage of a lamp was increased, usually the lamp envelope was also increased in size. In the fields mentioned above, the demand for higher wattage lamps increased to a point where thousands of watts were required.

The lamp industry overcame this problem of increased lamp size by using quartz envelopes and halogen fills so that wattage could be increased while using smaller envelopes. However, in the fabrication of the seal of large wattages having smaller envelope size a more perplexing problem of heat was encountered.

Briefly, in the fabrication of quartz-halogen lamps of relative low wattage, the important sealing operation includes using wafer-thin strips of molybdenum as current conductors in the seal area. These strips were welded between a lead'in wire and a filament support wire. This assembly was fitted into a quartz tubular envelope and after heating of the quartz, a mechanical sealing die was brought into operation. This sealing operation pinched the area where the molybdenum strip bridged the lead-in wires and provided a vacuumtight seal. Normally, on all standard low wattage lamps, this sealing operation was adequate. But with the ever-increasing need for higher wattages the molybdenum foil strips could not wholly fulfill the need mainly due to the low thermal conductivity of quartz glass. A continuous heat buildup in the foil caused a voltage drop across the seal. For example, a voltage drop of as much as 1.5 volts in a 21v.-l50w. iodine-quartz lamp was noticed. Due to this change, a higher voltage was needed to give the required light output. Most filaments are designed to operate at their maximum electrical capacity and therefore it was necessary to process them to withstand the added surges of starting voltages. In recent developments such as disclosed in copending application to Gates et al., Ser. No. 596,908 and assigned to the same assignee, a new method of scaling is disclosed. In the Gates application molybdenum cups are utilized as sealing and conductor supporters. The top half of each cup is encapsulated within a quartz sleeve attached to the base dies of the lamp, leaving the base portion of the cup exposed. The exposed base of each cup is provided with a centrally located aperture for the location of a filament-supporting conducting rod that is brazed or heliarc welded in place. This provides an unrestricted current-carrying path to the filament of the lamp. With this arrangement, the problems encountered with former current-carrying conductor seals were eliminated.

With all of the above-mentioned advancements in seal design, the major problem of heat buildup in the seal area which was due directly to heat radiated from the filament, restricted the optimum use of these high wattage lamps.

SUMMARY OF THE INVENTION In my improved method I have overcome the overheating in the seal area of the lamp. I utilize a reflective coating that is placed between the filament assembly and the seal areas. The

coating possesses a high melting point, is nonvolatile, has a low vapor pressure and has high reflectivity, such as zirconium oxide.

1 have found that by coating the external surface of the base disc with the oxide, the heat generated by the filament assembly is reflected away from the critical seal areas. The coating also reflects random light rays back into the optical system.

DESCRIPTION OF THE DRAWING In the drawing an elevational cross-sectional view of a high wattage lamp of my invention is shown.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a completed lamp assembly is illustrated partly in cross section. The lamp is a typical high wattage quartz-iodine lamp where a unique sealing method is utilized. A complete description of the sealing method is disclosed in the copending application of Gates, Ser. No. 596,908.

Briefly in the sealing of a lamp of this type, a pair of refractory metal cups [0 are first encapsulated in glass jackets 12, thereafter the bottom half of the glass is then removed from the cups and the encapsulated top of the cups are then fused to quartz sleeves 14. These formed cup subassemblies 28 are then fitted into spaced-apart receiver holes in a flat base quartz disc 16 and fused in place, where the moly cups extend below the disc 16. The bottom of the moly cups 10 are provided with central openings for the passage and attachment of conductor rods 20, the upper portion of the rods are formed to support a filament assembly 22.

Thereafter a suitable quartz envelope 24 is placed over the filament assembly and is fused to the perimeter of the base disc 16. A filling and tipping operation is then initiated and, by way of conventional exhaust tube 26, the filament assembly 22 is hermetically sealed within the envelope 24 to complete the fabrication of the lamp.

The completed lamp as shown in the drawing allows separate current-carrying paths through the seal cup assemblies 28 to the filament assembly 22.

The separate paths permit high current usage of this type of lamp. As mentioned above, during excessive high current utilization of the lamp, the seal cup assemblies 28 tend to break down due to continual exposure to radiated heat generated from the filament assembly.

I have overcome this disadvantage by providing a reflective coating 30 on the exterior surface of the base disc 16. The reflective coating 30 separates the filament assembly 22 from the critical seal assemblies 28. There are many types of reflective coatings that can be used such as zirconia, alumina, titania or similar refractory materials. These oxides are nonvolatile, have a high melting point, a low vapor pressure and a highly reflective surface.

The coating I prefer to use is basically a zirconium oxide powder that is mixed with isopropyl alcohol or a similar organic solvent to form a slurry having the thickness of paint. This slurry can be applied to the exterior surface of the base disc with a brush and allowed to air-dry for approximately 2 minutes.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

lclaim:

1. An incandescent lamp comprising:

a quartz glass envelope;

a filament disposed in said envelope;

a quartz disc fused to one end of said envelope;

means forming an aperture in said disc;

a quartz sleeve fused to said lower surface of said disc and about the perimeter of said aperture;

a metal cup sealed to the lower edge of said sleeve;

means forming an aperture in said cup;

a rod disposed in said aperture of said cup;

a portion of said rod extending below the base of said cup;

the other end of said rod passing through said sleeve and the aperture in said disc and supporting said filament in said envelope;

a reflective refractory oxide coating positioned on the exterior surface of said disc separating said filament from said cup whereby said heat generated by said filament is reflected away from said cup.

2. The lamp according to claim 1 wherein said refractory oxide coating is nonvolatile, has a high melting point, a low vapor pressure and high reflectivity.

3. The lamp according to claim 2 wherein said coating is zirconium oxide.

4. An incandescent lamp comprising: a quartz glass envelope; a filament disposed in said envelope; a quartz disc fused to one end of said envelope; means forming a first aperture in said disc; a first quartz sleeve fused at one end to the lower surface of said disc and about the perimeter of said first aperture; a first quartz jacket sealed to the other end of said first quartz sleeve; a first metal cup sealed to said first quartz sleeve, said first cup having a first aperture at the bottom thereof; a first rod disposed in said first aperture of said first cup, a portion of said first rod extending below the base of said first cup, the other end of said first rod passing through said first sleeve into said first aperture in said disc and supporting one end of said filament; means forming a second aperture in said disc; a second quartz sleeve fused at one end to the lower surface of said disc and about the perimeter of said second aperture; a second quartz jacket sealed to the other end of said second quartz sleeve; a second metal cup sealed to said second quartz sleeve, said second cup having a second aperture at the bottom thereof; a second rod disposed in said second aperture of said second cup, a portionof said second rod extending below the base of said second cup, the other end of said second rod passing through said second sleeve into said second aperture in said disc and supporting the other end of said filament; a reflective refractory oxide coating disposed on the exterior surface of said disc thereby separating said filament from said first and second cups whereby said heat generated by said filament is reflected away from said first and second cups.

5. The lamp according to claim 4 wherein said refractory oxide coating is nonvolatile, has a high melting point, a low vapor pressure and high reflectivity.

6. The lamp according to claim 2 wherein said coating is zirconium oxide. 

